With the ubiquity of the Internet and computer networks, electronic mail (email) has become the preferred method of communicating textual, graphical and other digital information. Unlike conventional postal mail, email may arrive at its destination within seconds or minutes of its sending, even where the recipient is across the globe. Moreover, an email may be easily sent to multiple recipients. Most enterprise service providers now support an email application program providing email accounts for its subscribers.
A conventional email system operates using a mail user agent which is a software application program used to send and receive emails. Examples include Outlook® messaging and collaboration client and Hotmail® web-based e-mail service by Microsoft® Corporation, Redmond, Wash. Regardless of whether local or web-based, mail user agents have conventionally not been extensible. That is, conventional mail user agents do not allow significant interactivity with web servers over the World Wide Web. While it is common to embed URL addresses within an email, once a URL is selected, the user is taken from the mail user agent, and the user accesses the selected web server URL via the user's browser. Further interaction with the selected URL is then performed by the browser, outside of the mail user agent.
Some truly extensible mail user agents are known which allow access to a web server from within the mail user agent. However, allowing a web server's script to run within a mail user agent presents security and operational issues for the host computing system (the user's computing device or enterprise service provider). Once run within the mail user agent on the host computing system, a web server's script could potentially impair or interfere with the operation of one or more applications on the host computing system. Worse still, the web server could run malevolent code from within the mail user agent which could infect the host system, steal data, etc. As such, prior art email systems do not allow unrestricted extensible interactivity over the Internet. Instead, such systems set up virtual sub-networks, where those entities wishing to provide interactive content via the extensible email system are prescreened and authenticated. Only then are they admitted to the virtual sub-network and allowed to provide interactive content via the mail user agent.